# Curl 8 19 0 > CLI tool and C library for multi-protocol data transfers supporting HTTP/HTTPS, FTP, SFTP, and 30+ protocols. Covers command-line usage, authentication, proxies, SSL/TLS, and WebSocket support. Use when making HTTP requests from the terminal, writing scripts that download/upload data, building C applications with libcurl, or working with curl's supported protocols. - Skill: `tangledgroup/curl-8-19-0` (Agent Skill, multi-file: 7 files) - Install (CLI): `npx skillmds@latest add tangledgroup/curl-8-19-0` - Raw SKILL.md: https://api.skillmd.com/api/skills/tangledgroup/curl-8-19-0/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - License: MIT - Author: tangledgroup (https://skillmd.com/u/tangledgroup) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tangledgroup/curl-8-19-0 --- # curl 8.19.0 ## Overview curl is a command-line tool and library (libcurl) for transferring data with URLs. It supports over 30 protocols including HTTP, HTTPS, FTP, FTPS, SFTP, SCP, IMAP, SMTP, POP3, LDAP, MQTT, RTMP, SMB, TELNET, TFTP, DICT, GOPHER, and FILE. libcurl provides a C API with easy, multi, share, URL, MIME, header, and WebSocket interfaces used by applications across 101 operating systems and 28 CPU architectures. curl handles persistent connections, SOCKS proxies, HTTP/2 multiplexing, HTTP/3 (QUIC), TLS with multiple backends (OpenSSL, GnuTLS, wolfSSL, mbedTLS, rustls, Schannel, Secure Transport), authentication methods (Basic, Digest, NTLM, Negotiate/SPNEGO, Kerberos), cookie jars, content encoding (gzip, deflate, brotli, zstd), and much more. ## When to Use - Making HTTP(S) GET/POST/PUT/DELETE requests from the command line - Downloading or uploading files via HTTP, FTP, SFTP, SCP, SMB - Scripting data transfers with URL globbing, parallel downloads, and config files - Building C applications that need network transfer capabilities via libcurl - Working with mail protocols (IMAP, SMTP, POP3) from the command line or C code - Implementing WebSocket communication in C applications - Performing multi-protocol transfers with authentication, proxies, and TLS - Parsing and manipulating URLs programmatically with the libcurl URL API ## Core Concepts **URL syntax**: curl follows "RFC 3986 plus" — grounded in RFC 3986 with pragmatic deviations for real-world URLs. Supports scheme-less URLs (guesses protocol from hostname prefix), allows one to three slashes after the colon, percent-encodes non-ASCII bytes, and handles spaces in `Location:` headers by re-encoding to `%20`. **Globbing**: The CLI supports URL ranges `[N-M]` and lists `{one,two,three}` for batch transfers. Use `-g`/`--globoff` to disable globbing (needed for IPv6 bracket addresses in URLs). **Persistent connections**: When multiple URLs share the same host on one command line, curl reuses the TCP connection. This applies across protocols and is automatic — no special option needed. **Protocol guessing**: Without an explicit scheme, curl guesses from hostname prefix: `ftp.` → FTP, `dict.` → DICT, `ldap.` → LDAP, `imap.` → IMAP, `smtp.` → SMTP, `pop3.` → POP3, everything else → HTTP. ## Installation / Setup curl is typically pre-installed on Linux and macOS. On Unix, build from source: ```bash ./configure --with-openssl [--with-gnutls --with-wolfssl] make make test # optional sudo make install ``` For custom install paths: ```bash ./configure --prefix=$HOME/curl-install --with-openssl make && make install ``` Use `curl-config` to query build features and linker flags: ```bash curl-config --cflags # compiler include flags curl-config --libs # linker flags curl-config --feature # enabled features (SSL, HTTP2, etc.) curl-config --protocols # supported protocols ``` ## Usage Examples **Basic downloads:** ```bash # GET a webpage to stdout curl https://www.example.com/ # Save with custom filename curl -o page.html https://www.example.com/ # Save with remote filename curl -O https://www.example.com/file.txt # Multiple files with remote names curl -O https://example.com/a.txt -O https://example.com/b.txt ``` **POST data:** ```bash # URL-encoded form POST curl -d "name=Rafael&phone=3320780" https://www.example.com/guest.cgi # Auto URL-encode POST data curl --data-urlencode "name=Rafael Sagula&phone=3320780" https://www.example.com/guest.cgi # Multipart form with file upload curl -F "file=@cooltext.txt" -F "yourname=Daniel" https://www.example.com/postit.cgi # Form string (safe for untrusted input, no @ interpretation) curl --form-string "comment=Hello @world" https://www.example.com/post ``` **Authentication:** ```bash # HTTP Basic auth curl -u user:passwd https://example.com/ # Auto-negotiate most secure auth method the server supports curl --anyauth -u user:passwd https://example.com/ # SFTP with SSH key curl -u username --key ~/.ssh/id_rsa sftp://example.com/etc/issue # SCP with password-protected key curl -u username: --key ~/.ssh/id_rsa --pass key_password scp://example.com/~/file.txt ``` **Upload:** ```bash # FTP upload curl -T uploadfile -u user:passwd ftp://ftp.example.com/myfile # HTTP PUT curl -T file https://www.example.com/myfile # Append to remote file (FTP) curl -T localfile -a ftp://ftp.example.com/remotefile ``` **Headers and verbose output:** ```bash # Include response headers in output curl -i https://example.com/ # Save headers to file curl --dump-header headers.txt https://example.com/ # HEAD request (headers only) curl -I https://example.com/ # Add custom header curl -H "X-Custom-Header: value" https://example.com/ # Suppress internal header (e.g., Host:) curl -H "Host:" https://example.com/ # Verbose protocol trace curl -v https://example.com/ # Full hex+ASCII trace to file curl --trace-ascii trace.txt https://example.com/ ``` **Redirects and cookies:** ```bash # Follow redirects (default: up to 50) curl -L https://example.com/redirect # Save and reuse cookies curl -c cookies.txt https://example.com/ # save cookies curl -b cookies.txt https://example.com/other # load cookies curl -b cookies.txt -c cookies.txt https://example.com/ # read+write same file ``` **Speed limits and timeouts:** ```bash # Abort if speed drops below 3000 bytes/sec for 60 seconds curl -Y 3000 -y 60 https://far-away.example.com # Throttle to 10KB/s max curl --limit-rate 10K https://example.com/largefile # Total time limit: 30 minutes curl -m 1800 https://example.com/ ``` **Range requests:** ```bash # First 100 bytes (HTTP byte range) curl -r 0-99 https://www.example.com/ # Last 500 bytes curl -r -500 https://www.example.com/ ``` **Proxy:** ```bash # HTTP proxy curl -x proxy.example.com:8888 https://example.com/ # Proxy with authentication curl -U proxyuser:proxypass -x proxy:8888 https://example.com/ # SOCKS5 proxy curl --socks5 proxy.example.com:1080 https://example.com/ # No proxy for specific hosts curl --noproxy example.com,localhost -x proxy:8888 https://example.com/ ``` **Custom output with write-out:** ```bash # Print download size and HTTP status code curl -s -o /dev/null -w "Size: %{size_download} bytes, HTTP: %{http_code}\n" https://example.com/ ``` ## Advanced Topics **URL Syntax and Schemes**: URL parsing rules, scheme support, globbing, security considerations → [URL Syntax](reference/01-url-syntax.md) **libcurl Easy Interface**: Single-transfer C API, handle lifecycle, callbacks, options, error handling → [Easy Interface](reference/02-libcurl-easy.md) **libcurl Multi Interface**: Concurrent transfers in a single thread, socket-based event loop, poll API → [Multi Interface](reference/03-libcurl-multi.md) **SSL/TLS and Certificates**: TLS backends, certificate verification, client certs, HSTS, ECH, Alt-Svc → [SSL/TLS](reference/04-ssl-tls.md) **Protocols Reference**: Protocol-specific behaviors for HTTP, FTP, SFTP, IMAP, SMTP, POP3, MQTT, WebSocket → [Protocols](reference/05-protocols.md) **Security and Configuration**: Security best practices, .netrc, config files, environment variables, write-out format → [Security and Config](reference/06-security-config.md)